The examples of Pisces are true fishes whereas others are false fishes.
VVI Examples of PISCES for Entrance Exams of Nepal are:
- Scoliodon
- Zygaena
- Trygon
- Scoliodon (Dogfish, Viviparous fish)
- Torpedo (Electric Ray)
- Chimera (Ratfish)
- Labeo (Rohu)
- Hippocampus (Sea Horse)
- Bombay Duck
- Flying Fish (Exocoetus)
General Characteristics of Pisces
· They arose in the Silurian period and dominated during the Devonian period so it is called the golden age of fishes.· Their body is covered by mesodermal scales and dermal denticles or bony plates.
· They have slime gland on their skin
· They have no eyelids, neck, or tympanum.
· Presence of scroll valves in Elasmobranchii or shark which are the internal folds of the mucous membrane in the intestine for the absorption of food.
· Presence of Ampulla of Lorenzini which are the thermoreceptors found on the dorsal and ventral region of the head of the dogfish
· Presence of maltase cross trunk vertebrae. The Centrum of the vertebrae is supported by four wedge-shaped calcified fibro- cartilage which is arranged like the cross known as the maltase cross.
· Neuromast organs
· They are rheoreceptors of scoliodon. These are a collective form of the lateral line system for balancing and pit organs lie in the pits of the dorsal and lateral sides of the head.
Differences between Sharks and Ray fishes
| S.N | Sharks | Ray fishes |
|---|---|---|
| 1. | They mostly inhabit the open water and swim actively. | They mostly inhabit at bottom of the sea and are sluggish inhabit. |
| 2. | Their body is laterally compressed. | Their body is dorsoventrally flattened. |
| 3. | The tail fin is asymmetrical, well-developed, and not distinctly marked off from the trunk. | The tail fin is cylindrical pointed and distinctly marked off the body. |
| 4. | Gill slits are present at lateral sides of the body. | Gill slits are present on the ventral surface of the head. |
| 5. | Spiracles are mostly absent if present they are small and laterally present. | Spiracles are present on the dorsal side as a larger form. |
| 6. | The size of the pectoral fins is moderate and has a narrow base. | The size of pectoral fins is very large and present at the lateral sides of the head and trunk. |
| 7. | Example: Scoliodon, Zygaena | Example: Torpedo, Trygon, etc. |
Two Classes of Pisces
i. Chondrichthyes (Cartilaginous fishes), Elasmobranchiiii. Osteichthyes (Bony fishes), Teleostomi
| Characteristics | Chondrichthyes | Osteichthyes |
|---|---|---|
| i. Habitat | Exclusively marine | Marine and freshwater |
| ii. Mouth and nostrils | Ventral | Mouth: Terminal Nostrils: Dorsal |
| iii. Gill slits | 5-7 pairs, no operculum. | 5 pairs, covered with operculum. |
| iv. Caudal fin | Heterocercal | Homocercal |
| v. Endoskeleton | Cartilagenous | Bony |
| vi. Exoskeleton | Placoid scales (Dermal) | Cycloid (Circular), ctenoid (comb-like) Rhomboid scales, all bony |
| vii. Air bladder | Absent | Present |
| viii. Ampulla of Lorenzini (Thermoreceptor) | Present e.g: Scoliodon (Dogfish, viviparous fish) Torpedo (Electric Ray) Chimaera (Ratfish) | Absent e.g: Labeo (Rohu) Hippocampus (Sea Horse) |
Note: Isinglass is prepared from the air bladder of fishes.
· Shagreen is the dried skin of Elasmobranchii.
· Air bladder or swim bladder acts as the organ for buoyancy or hydrostatic organ.
· Lateral line system acts as sense organ or organ of equilibrium.
· Male Sea-horse has a brood pouch.
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